Method for preparing bamboo fibers and recycling black liquor

Abstract

The invention relates to the technical field of fiber preparation, in particular to a method for preparing bamboo fibers and recycling black liquor. The method comprises the steps that bamboo chips are placed in alkali liquor to be subjected to digestion, first solid-liquid separation is conducted, and bamboo fibers and black liquor are obtained; carrying out adsorption decoloration on the black liquor to obtain a decoloration solution; carrying out acidification on the decolored solution to separate out lignin, and carrying out second solid-liquid separation to obtain lignin and acidification wastewater; carrying out Fenton oxidation on the acid precipitation wastewater, and carrying out ion exchange desalination on the effluent to obtain purified water; and mixing the purified water with flushing wastewater, and recycling the obtained mixed water to the digestion process. The method not only solves the problem of environmental pollution of the traditional method, but also converts the by-product lignin into a marketable product, and is low in energy consumption.

Description

Technical Field

[0001] This invention relates to the field of fiber preparation technology, and in particular to a method for preparing bamboo fiber and utilizing black liquor resources. Background Technology

[0002] Traditional bamboo fiber production processes primarily rely on the alkaline method, which involves soaking bamboo in sodium hydroxide solution to separate components such as cellulose and lignin. However, this process presents significant environmental and resource utilization challenges. Firstly, the black liquor produced during alkaline treatment contains high concentrations of organic matter, residual alkali, and soluble lignin. Direct discharge of this liquor would severely pollute water bodies. Traditional treatment methods typically rely on complex downstream wastewater and residue treatment systems, such as alkali recovery boilers, multi-stage biological treatment, or evaporation concentration. These systems are not only energy-intensive and complex, but also have high costs for large-scale production. Furthermore, post-treatment processes may generate other byproducts or side effects (such as the high-salt environment of evaporation concentration and gas generation in biological treatment ponds). Secondly, lignin in the black liquor is a high-value-added byproduct. Most processes only utilize the lignin combustion capacity, failing to effectively separate and recover high-purity lignin, leading to resource waste. Although some studies have attempted to extract lignin through acid precipitation, secondary pollution often results due to insufficient process integration or incomplete subsequent wastewater treatment. Additionally, traditional processes require frequent pH adjustments, increasing chemical consumption and reducing production efficiency, making it difficult to meet the demands of modern green manufacturing. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for preparing bamboo fiber and utilizing black liquor resources. This invention not only solves the environmental pollution problem of traditional methods, but also converts the by-product lignin into a marketable product, and has low energy consumption.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing bamboo fiber and utilizing black liquor resources, comprising the following steps: soaking bamboo chips in an alkaline solution, performing a first solid-liquid separation to obtain crude bamboo fiber and black liquor; The crude bamboo fiber is washed to obtain pure bamboo fiber and rinsing wastewater; The black liquor is purified to obtain purified water; The purified water is mixed with the rinsing wastewater, and the resulting mixed water is reused in the soaking and boiling process. The purification process employs either method 1 or method 2. Method 1 includes the following steps: The black liquor is adsorbed and decolorized to obtain a decolorized liquid; the decolorized liquid is acid-precipitated to precipitate lignin, followed by a second solid-liquid separation to obtain lignin and acid-precipitated wastewater; the acid-precipitated wastewater is then subjected to Fenton oxidation and desalinated by ion exchange to obtain purified water; Method 2 includes the following steps: The black liquor is subjected to acid precipitation to precipitate lignin, followed by a second solid-liquid separation to obtain lignin and acid precipitation wastewater. The acid precipitation wastewater is then subjected to adsorption decolorization, ion exchange desalination, and ozone oxidation to obtain purified water.

[0005] Preferably, the alkaline agent in the alkaline solution is sodium hydroxide, or a sodium hydroxide-sodium sulfite composite alkaline agent, or a sodium hydroxide-sodium sulfide composite alkaline agent, or a sodium hydroxide-urea composite alkaline agent; When the alkali is sodium hydroxide, the mass concentration of the alkali solution is 8-12%; when the alkali is a sodium hydroxide-sodium sulfite composite alkali, the mass concentration of sodium hydroxide in the alkali solution is 6-12%, and the mass concentration of sodium sulfite is 0.5-1.5%; when the alkali is a sodium hydroxide-sodium sulfide composite alkali, the mass concentration of sodium hydroxide in the alkali solution is 6-12%, and the mass concentration of sodium sulfide is 0.5-2%; when the alkali is a sodium hydroxide-urea composite alkali, the mass concentration of sodium hydroxide in the alkali solution is 8-12%, and the mass concentration of urea is 12-15%. When the alkali is sodium hydroxide, or a sodium hydroxide-sodium sulfite composite alkali, or a sodium hydroxide-sodium sulfide composite alkali, the soaking includes: first soaking at 90-105℃ for 3-4 hours, then keeping warm at not less than 80℃ for 1-2 hours, and finally soaking at 90-105℃ for 3-4 hours. When the alkali is a sodium hydroxide-urea composite alkali, the soaking includes: first, soaking and stirring at a constant temperature of 65±1℃ for 8-10 hours, and then turning off the power and keeping it warm for 1.5-4 hours.

[0006] Preferably, the adsorbent used for adsorption and decolorization includes activated carbon or macroporous adsorption resin.

[0007] Preferably, when purification is performed using method 1, the acid precipitation is a first-stage acid precipitation; The temperature of the first-stage acid precipitation is 40-60℃, the pH value is 2-4, and the time is 1-2h; When method 2 is used for purification, the acid precipitation is a two-stage acid precipitation; The two-stage acid precipitation includes a first acid precipitation and a second acid precipitation performed sequentially; the temperature of the first acid precipitation is 35-40℃, the pH value is 4-5, and the time is 3-4h; the temperature of the second acid precipitation is 40-60℃, the pH value is 2, and the time is more than 6h.

[0008] Preferably, the ozone oxidation includes: adjusting the pH value of the acid precipitation wastewater to 9-10, and aerating the acid precipitation wastewater with ozone in the presence of a catalyst; the ozone oxidation time is 1-2 hours; and the mass concentration ratio of ozone to COD is 4-5:1.

[0009] Preferably, the Fenton oxidation is a homogeneous Fenton oxidation or a heterogeneous Fenton oxidation; The conditions for the homogeneous Fenton oxidation include: Fe 2+ The dosage is 0.22-1.5 g / L, the dosage of hydrogen peroxide solution is 0.5-4 g / L, and the pH value is 2-4; The conditions for the heterogeneous Fenton oxidation include: an iron-based catalyst dosage of 0.5-2 g / L, a hydrogen peroxide solution dosage of 2-4 g / L, and a pH value of 2-4. The mass concentration of the hydrogen peroxide solution is 30%.

[0010] Preferably, the process parameters for Fenton oxidation, ozone oxidation, and acid precipitation are controlled intelligently.

[0011] Preferably, the second solid-liquid separation includes pressure filtration or rotary vibrating screen filtration.

[0012] Preferably, the ion exchange desalination includes sequentially removing Na+ using a strongly acidic cation exchange resin. + Removal of Cl with weakly basic anion exchange resin - .

[0013] Preferably, the amount of water added during soaking and the soaking temperature are controlled by a PLC.

[0014] This invention provides a method for preparing bamboo fiber and utilizing black liquor resources, comprising the following steps: soaking bamboo chips in an alkaline solution, performing a first solid-liquid separation to obtain crude bamboo fiber and black liquor; washing the crude bamboo fiber to obtain pure bamboo fiber and rinsing wastewater; purifying the black liquor to obtain purified water; mixing the purified water with the rinsing wastewater, and reusing the resulting mixed water in the soaking process; the purification adopts method 1 or method 2; method 1 comprises the following steps: adsorbing and decolorizing the black liquor to obtain a decolorized solution; acidifying the decolorized solution to precipitate lignin, performing a second solid-liquid separation to obtain lignin and acidified wastewater; subjecting the acidified wastewater to Fenton oxidation followed by ion exchange desalination to obtain purified water; method 2 comprises the following steps: acidifying the black liquor to precipitate lignin, performing a second solid-liquid separation to obtain lignin and acidified wastewater; subjecting the acidified wastewater to adsorption decolorization, ion exchange desalination, and then ozone oxidation to obtain purified water.

[0015] This invention has the following advantages: The entire process is designed for zero waste. This invention integrates black liquor decolorization, acid precipitation to recover lignin, oxidation treatment, and recycled water reuse, achieving complete resource utilization of wastewater and waste residue in bamboo fiber production and completely solving the environmental pollution problems of traditional processes. The entire process requires only a small amount of water to maintain operation, truly meeting the requirements of clean production.

[0016] Diversified output of high-value products. This invention innovatively transforms "waste" from the process into high-value-added products: the lignin recovered from acid precipitation can reach a purity of over 80%, which can be sold directly as a chemical raw material, or further processed into fertilizers and other products for use in the agricultural and forestry fields; the treated bamboo fiber has uniform and stable quality, making it suitable for the manufacture of high-end composite materials; the neutralized water formed by mixing purified water and rinsing wastewater fully meets the requirements of the production process.

[0017] Energy-efficient and high-performance process design. By optimizing the process, the high-energy-consuming black liquor evaporation and concentration stage in the traditional alkali recovery process is eliminated; by utilizing waste acid and waste alkali neutralization (the rinsing wastewater generated from washing crude bamboo fiber is waste alkali, and the downstream effluent of the heterogeneous Fenton oxidation process is acidic wastewater), energy and chemical consumption are significantly reduced; furthermore, the oxidation treatment unit adopts intelligent control to ensure treatment efficiency while minimizing the amount of reagents used.

[0018] Exceptional environmental performance. Compared to traditional processes, this invention can achieve approximately 60-70% internal water circulation in a single cycle, reducing fresh water consumption by more than 30%, significantly lowering overall energy consumption, and completely eliminating the discharge of toxic black liquor. No secondary pollution is generated during the process, all byproducts can be recycled, and the carbon footprint is significantly reduced compared to traditional methods, making it a truly green manufacturing technology.

[0019] Flexible industrial adaptability. The process parameters of this invention can be precisely controlled according to different raw material and product requirements, and the equipment investment is only 1 / 3 of that of traditional alkali recovery systems. The process is simple and clear, easy to build an intelligent control system, and easy to promote industrialization. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system used in the method for preparing bamboo fiber and utilizing black liquor resources according to the present invention. Detailed Implementation

[0021] This invention provides a method for preparing bamboo fiber and utilizing black liquor resources, comprising the following steps: soaking bamboo chips in an alkaline solution, performing a first solid-liquid separation to obtain crude bamboo fiber and black liquor; The crude bamboo fiber is washed to obtain pure bamboo fiber and rinsing wastewater; The black liquor is purified to obtain purified water; The purified water is mixed with the rinsing wastewater, and the resulting mixed water is reused in the soaking and boiling process. The purification process employs either method 1 or method 2. Method 1 includes the following steps: The black liquor is adsorbed and decolorized to obtain a decolorized liquid; the decolorized liquid is acid-precipitated to precipitate lignin, followed by a second solid-liquid separation to obtain lignin and acid-precipitated wastewater; the acid-precipitated wastewater is then subjected to Fenton oxidation and desalinated by ion exchange to obtain purified water; Method 2 includes the following steps: The black liquor is subjected to acid precipitation to precipitate lignin, followed by a second solid-liquid separation to obtain lignin and acid precipitation wastewater. The acid precipitation wastewater is then subjected to adsorption decolorization, ion exchange desalination, and ozone oxidation to obtain purified water.

[0022] In this invention, unless otherwise specified, all raw materials and equipment used are commercially available products well known in the art.

[0023] This invention involves soaking bamboo strips in an alkaline solution, followed by a first solid-liquid separation to obtain crude bamboo fiber and black liquor.

[0024] In this invention, the bamboo strips are preferably obtained from bamboo through pretreatment. The pretreatment method is not specifically required; any well-known pretreatment method in the art can be selected for different types of bamboo. Specifically, the bamboo can be moso bamboo, *Phyllostachys nigra*, or *Phyllostachys pubescens*. The silica slag produced during the bamboo pretreatment is preferably calcined to obtain precipitated silica (SiO2 content not less than 92%), conforming to the standard "Precipitated Hydrated Silica" (GB / T 20020-2013).

[0025] In this invention, the alkaline agent in the alkaline solution is preferably sodium hydroxide, or a sodium hydroxide-sodium sulfite composite alkaline agent, or a sodium hydroxide-sodium sulfide composite alkaline agent, or a sodium hydroxide-urea composite alkaline agent.

[0026] Those skilled in the art can flexibly select different combinations of alkali agents (such as single alkali or compound alkali) according to the characteristics of the target lignin product, which can significantly affect the chemical structure and functional groups of lignin. Lignin obtained by different alkali agents exhibits differences in bonding mode, solubility and yield. For example, sulfonation modification can enhance water solubility, while sulfurization treatment introduces specific sulfur groups, providing a diversified raw material basis for subsequent high-value applications.

[0027] The lignin products obtained from the four alkali agents are as follows: 1) The product after acid precipitation of black liquor from sodium hydroxide leaching is mainly alkali lignin (S-type lignin). The phenylpropane units are mainly composed of β-O-4 bonds (molar content of about 60%, that is, after acid precipitation, about 60% of the original "β-O-4 bonds" remain unbroken). It contains a small amount of condensation structure (molar content of about 15~20%, condensation structure mainly refers to condensation lignin (such as guaiac lignin propane, etc.), mainly carbon-carbon bonds, and also contains ether bonds). The acid precipitation yield is high, but the sulfur content of the lignin product is low (≤1.5%). 2) After acid precipitation of black liquor from sodium hydroxide-sodium sulfite leaching, the main product is sulfonated lignin (LS type), with the β-O-4 bond retention rate increased to 65-70%, and the addition of Cα sulfonic acid groups (0.3~0.6 mmol / g), resulting in improved acid precipitation yield and enhanced water solubility of lignin (solubility at 25℃ >50 g / L); after acid precipitation of black liquor from sodium hydroxide-urea leaching, the main product is sulfonated lignin (crude lignin sulfonate). 3) After acid precipitation of black liquor from sodium hydroxide-sodium sulfide leaching, the main product is sulfolidin (containing thioether bonds and thiophene structures, mainly sulfate lignin), with the β-O-4 bond retention rate decreasing to 50-55% and the condensation structure increasing to 25-30%.

[0028] In this invention, when the alkali is sodium hydroxide, the mass concentration of the alkali solution is preferably 8-12%, and in specific embodiments it can be 8%, 9%, 10%, 11% or 12%.

[0029] When the alkali is a sodium hydroxide-sodium sulfite composite alkali, the mass concentration of sodium hydroxide in the alkali solution is preferably 6-12%, and in specific embodiments it can be 6%, 7%, 8%, 9%, 10%, 11% or 12%; the mass concentration of sodium sulfite is preferably 0.5%.

[0030] When the alkali is a sodium hydroxide-sodium sulfide composite alkali, the mass concentration of sodium hydroxide in the alkali solution is 6-12%, and in specific embodiments it can be 6%, 7%, 8%, 9%, 10%, 11% or 12%; the mass concentration of sodium sulfide is preferably 2%.

[0031] When the alkaline agent is sodium hydroxide, or a sodium hydroxide-sodium sulfite composite alkaline agent, or a sodium hydroxide-sodium sulfide composite alkaline agent, the soaking process preferably includes: first soaking at 90-105℃ for 3-4 hours (referred to as the first soaking), then maintaining a temperature at not less than 80℃ for 1-2 hours (referred to as the second soaking, which refers to maintaining a temperature with the power off after the first soaking), and finally soaking at 90-105℃ for 3-4 hours (referred to as the third soaking). In specific embodiments, the temperatures of the first and third soakings can independently be 90, 95, 100, or 105℃.

[0032] When the alkali is a sodium hydroxide-urea composite alkali, the mass concentration of sodium hydroxide in the alkali solution is preferably 8-12%, and in specific embodiments it can be 8%, 9%, 10%, 11% or 12%; the mass concentration of urea is preferably 12-15%, and in specific embodiments it can be 12%, 13%, 14% or 15%; the soaking process preferably includes: first, soaking and stirring at a constant temperature of 65±1℃ for 8-10 hours, and then turning off the power and keeping it at a constant temperature for 1.5-4 hours. The stirring rate is preferably 50-100 rpm.

[0033] In this invention, the soaking is preferably carried out in a reaction vessel made of corrosion-resistant material, such as a stainless steel reaction vessel.

[0034] In this invention, the first, second, and third soaking processes are preferably carried out under stirring conditions. This invention does not have special requirements for the stirring rate; any stirring rate well-known in the art can be used. This invention employs segmented soaking, enabling efficient extraction and preparation of bamboo fiber. Furthermore, compared to constant-temperature soaking, the segmented soaking method significantly saves energy consumption while maintaining a high fiber yield, and the time required is similar to that of constant-temperature soaking.

[0035] In this invention, the amount of water added during soaking and the soaking temperature are preferably controlled by a PLC. In specific embodiments, a soaking oven with built-in PLC infrared temperature control function can be used to achieve temperature control, such as the commercially available brand model ZN-QFD; the PLC automatic water replenishment can be controlled by a commercially available brand model Siemens S7-1200 PLC.

[0036] The present invention does not have any special requirements for the first solid-liquid separation method. A solid-liquid separation method well known in the art can be used. In the embodiments of the present invention, the bamboo fiber crude product is directly taken out using a hanging basket to achieve the separation of the bamboo fiber crude product and the black liquor.

[0037] After obtaining the crude bamboo fiber, the present invention washes the crude bamboo fiber to obtain pure bamboo fiber and rinsing wastewater.

[0038] The present invention does not have any special requirements for the washing process, and any washing process known in the art is acceptable.

[0039] Before washing, the present invention preferably further includes crushing the coarse bamboo fiber product, washing and draining it, and then opening and sorting it to obtain a usable bamboo fiber product.

[0040] In this invention, the pH value of the rinsing wastewater is preferably 9-10, and it can be recycled and reused.

[0041] After obtaining the black liquor, the present invention purifies the black liquor to obtain purified water.

[0042] In this invention, the purification is performed using method 1 or method 2.

[0043] Method 1 includes: adsorbing and decolorizing the black liquor to obtain a decolorized liquid; acidifying the decolorized liquid to precipitate lignin, followed by a second solid-liquid separation to obtain lignin and acidified wastewater; and subjecting the acidified wastewater to Fenton oxidation followed by ion exchange desalination to obtain purified water.

[0044] The present invention adsorbs and decolorizes the black liquor to obtain a decolorized liquid.

[0045] Before the adsorption and decolorization process, the black liquor is preferably filtered to remove impurities. In this invention, the filtration and impurity removal can specifically employ a vibrating screen (such as an XZS-800 vibrating screen) or a ceramic membrane for impurity removal.

[0046] In this invention, the adsorbent used for adsorption decolorization includes activated carbon or macroporous adsorption resin; this invention does not have special requirements for the adsorption decolorization process, and a decolorization process well known in the art can be used. This invention purifies black liquor through adsorption decolorization, ensuring the stability of subsequent treatment.

[0047] After obtaining the decolorizing liquid, the present invention performs acid precipitation on the decolorizing liquid to precipitate lignin, followed by a second solid-liquid separation to obtain lignin and acid precipitation wastewater.

[0048] In this invention, the acid precipitation is preferably a first-stage acid precipitation.

[0049] In this invention, the preferred temperature for the first-stage acid precipitation is 40-60℃, the preferred pH value is 2-4, and the preferred precipitation time is 1-2 hours. In specific embodiments, the temperature for the first-stage acid precipitation can be 40, 45, 50, 55, or 60℃, the pH value can be 2, 2.5, 3, 3.5, or 4, and the precipitation time can be 1, 1.5, or 2 hours.

[0050] In this invention, sulfuric acid or phosphoric acid is preferably added for the acid precipitation; the mass fraction of the sulfuric acid is preferably 98%; and the mass fraction of the phosphoric acid is preferably 85%.

[0051] In this invention, the acid and alkali reagents added during acid precipitation and the amount of water replenished (the solid matter will carry out a large amount of water during the acid precipitation process) are preferably controlled by a PLC.

[0052] In this invention, the second solid-liquid separation preferably includes pressure filtration or vibrating screen filtration. When pressure filtration is used, plate and frame filter press is preferred, and the preferred filtration conditions include: temperature 40-85°C, filter cloth pore size 50-100 micrometers, and plate and frame filter press pressure 0.4-0.8 MPa. Before the second solid-liquid separation, polyacrylamide (PAM) is preferably added to the waste liquid to be separated after acid precipitation. In this invention, the added mass of polyacrylamide is preferably 1% of the mass of the waste liquid to be separated. This invention accelerates lignin coagulation by adding an appropriate amount of PAM.

[0053] This invention achieves efficient separation and dehydration of lignin by precisely controlling the pH, temperature, and precipitation time during acid precipitation. The resulting lignin product has a low moisture content (≤12%), meeting the standard of "Industrial Lignin" (GB / T 31765-2015). It can be sold directly as a rubber reinforcing agent or asphalt modifier, significantly increasing the added value of by-products. It can also be further processed to obtain fertilizers and other products for use in agriculture and forestry.

[0054] After obtaining lignin, the present invention preferably further includes drying the lignin; the drying is preferably air-flow drying. In the present invention, the purity of the lignin after air-flow drying can reach more than 80%, meeting the first-grade standard of "Industrial Lignin" (GB / T 31765-2015).

[0055] After obtaining the acid precipitation wastewater, the present invention performs Fenton oxidation on the acid precipitation wastewater.

[0056] The Fenton oxidation is either homogeneous or heterogeneous.

[0057] In this invention, the conditions for homogeneous Fenton oxidation preferably include: Fe 2+ The dosage is 0.22-1.5 g / L, the hydrogen peroxide solution dosage is 0.5-4 g / L, and the pH value is 2-4; in specific embodiments, Fe 2+ The dosage can be 0.223, 0.5, 0.8, 1.1, 1.3 or 1.5 g / L, the dosage of hydrogen peroxide solution can be 1, 1.5, 2, 3, 3.2, 3.5 or 4 g / L, and the pH value can be 2, 2.5, 3, 3.5 or 4.

[0058] In this invention, the preferred conditions for the heterogeneous Fenton oxidation include: an iron-based catalyst dosage of 0.5-2 g / L, a hydrogen peroxide solution dosage of 2-4 g / L, and a pH value of 2-4. In specific embodiments, the iron-based catalyst dosage can be 0.5, 1, 1.5, or 2 g / L, the hydrogen peroxide solution dosage can be 2, 2.5, 3, 3.2, 3.5, or 4 g / L, and the pH value can be 2, 2.5, 3, 3.5, or 4.

[0059] In this invention, the mass concentration of the hydrogen peroxide solution is preferably 30%.

[0060] In this invention, the Fenton oxidation is preferably carried out under stirring conditions at room temperature (18-35°C).

[0061] In this invention, when homogeneous Fenton oxidation is used, after the Fenton oxidation is completed, the invention preferably further includes adding NaOH to the reaction system to adjust the pH to 6.8-9, which is used to precipitate iron ions and filter out the generated iron sludge.

[0062] After the oxidation is completed, the present invention performs ion exchange desalination on the resulting oxidized wastewater to obtain purified water.

[0063] In this invention, the ion exchange desalination preferably includes sequentially removing Na using a strongly acidic cation exchange resin. + Removal of Cl with weakly basic anion exchange resin - .

[0064] In this invention, the strongly acidic cation exchange resin can specifically be of type 001×7, and the weakly basic anion exchange resin can specifically be of type D301.

[0065] In this invention, Na + It is a product of the introduction of sodium hydroxide. Part of the chloride ions come from the bamboo itself, and a small part comes from the introduction of exogenous reagents during industrial catalysis or soaking process.

[0066] After ion exchange desalination, the resulting purified water contains Na + ≤5 mg / L, Cl - ≤10 mg / L.

[0067] The second purification method (method 2) will be explained below.

[0068] In this invention, method 2 includes: acid precipitation of the black liquor to precipitate lignin, followed by a second solid-liquid separation to obtain lignin and acid precipitation wastewater; and adsorption decolorization, ion exchange desalination, and ozone oxidation of the acid precipitation wastewater to obtain purified water.

[0069] The present invention involves acid precipitation of the black liquor to precipitate lignin, followed by a second solid-liquid separation to obtain lignin and acid precipitation wastewater.

[0070] In this invention, the acid precipitation is preferably a two-stage acid precipitation; the two-stage acid precipitation preferably includes a first acid precipitation and a second acid precipitation performed sequentially; the temperature of the first acid precipitation is preferably 35-40℃, the pH value is preferably 4-5, and the time is preferably 3-4h; the temperature of the second acid precipitation is preferably 40-60℃, and in specific embodiments it can be 40, 50 or 60℃, the pH value is preferably 2, and the time is preferably more than 6h, more preferably 6-12h.

[0071] This invention first uses a first acid to precipitate hemicellulose, and then uses a second acid to precipitate lignin. This ensures the lignin precipitation rate on the one hand, and prevents the hemicellulose from consuming large amounts of ozone during subsequent ozone oxidation, thus guaranteeing the ozone's oxidation effect on COD.

[0072] After obtaining the acid precipitation wastewater, the present invention performs adsorption decolorization, ion exchange desalination and ozone oxidation on the acid precipitation wastewater to obtain purified water.

[0073] In this invention, the conditions for adsorption decolorization and ion exchange desalination are the same as in method 1, and will not be repeated here.

[0074] In this invention, the ozone oxidation preferably includes: adjusting the pH of the acid precipitation wastewater to 9-10, and aerating the acid precipitation wastewater with ozone in the presence of a catalyst; the ozone oxidation time is preferably 1-2 hours; and the mass concentration ratio of ozone to COD is preferably 4-5:1. This invention preferably uses microporous aeration heads to generate tiny ozone bubbles; in this invention, the catalyst can be commercially available manganese dioxide or copper oxide industrial catalysts.

[0075] The reason why this invention performs adsorption decolorization and ion exchange desalination before ozone oxidation is that the ozone oxidation process has high requirements for water quality conditions. This invention performs adsorption decolorization and ion exchange desalination first, and then performs ozone oxidation last. This can ensure the oxidation effect, reduce the amount of ozone used, and reduce costs.

[0076] It is worth noting that when ozone oxidation is used, this invention preferably introduces oxygen into the black liquor during soaking to increase the dissolved oxygen content. The increased dissolved oxygen accelerates the degradation of lignin to form crude bamboo fiber and also synergizes with the oxidizing effect of ozone. This invention preferably introduces oxygen at 100-105°C, and the oxygen introduction amount is preferably 0.1-0.3 MPa, which can be 0.1, 0.2, or 0.3 MPa in specific embodiments.

[0077] Whether using Fenton oxidation or ozone oxidation, the oxidation process parameters (ozone input, pH, temperature, and water volume) are preferably controlled intelligently. This invention achieves automated reagent dosing and real-time monitoring through intelligent control.

[0078] This invention integrates high-precision sensors and a PLC control system to achieve fully automated management of the entire process, including soaking, pH adjustment, and water replenishment. The system features fast response, stable parameter control, and supports long-term data storage and remote monitoring, significantly improving production efficiency and process reproducibility. Through a PID algorithm, it achieves: 1) soaking temperature control accuracy ±0.5℃; 2) pH adjustment response time ≤20s; 3) water replenishment control accuracy ±2%. The system can store three years of operational data and supports remote monitoring (compliant with GB / T34036-2017 Industrial Automation System Standard).

[0079] After oxidation, the COD and suspended solids content in the wastewater decreased significantly.

[0080] After obtaining purified water, the present invention mixes the purified water with the aforementioned rinsing wastewater, and the resulting mixed water is reused in the soaking and boiling process, which significantly increases the annual water saving.

[0081] In this invention, when the oxidation process uses heterogeneous Fenton oxidation, the effluent from the oxidation process is acidic, and the resulting mixed water has a pH close to neutral; when the oxidation process uses ozone oxidation or homogeneous Fenton oxidation, the effluent from the oxidation process is close to neutral, and the resulting mixed water has a pH close to alkaline, with a pH value around 10.

[0082] In this invention, after the strongly acidic cation exchange resin and the weakly basic anion exchange resin are deactivated, the invention preferably further includes regenerating them. In this invention, the strongly acidic cation exchange resin is preferably regenerated countercurrently with hydrochloric acid; the weakly basic anion exchange resin is preferably regenerated cocurrently with a strong sodium oxide solution. In embodiments of this invention, the strongly acidic cation exchange resin is specifically regenerated countercurrently with 2.1% HCl (flow rate 4 BV / h), and the weakly basic anion exchange resin is specifically regenerated cocurrently with 2.0% NaOH (preheated to 42°C). This invention can recover sodium chloride through resin regeneration, achieving the dual goals of "pollution control and resource recovery".

[0083] The invention has been verified through large-scale pilot-scale tests. The process has shown excellent performance in terms of fiber yield, lignin recovery rate and water recycling rate, and the overall energy consumption has been greatly reduced, providing a reliable basis for industrial promotion.

[0084] Figure 1 This is a schematic diagram of the system used in the method for preparing bamboo fiber and utilizing black liquor resources according to the present invention. Figure 1As shown, this invention involves soaking bamboo strips in an alkaline solution, followed by a first solid-liquid separation to obtain crude bamboo fiber and black liquor. The crude bamboo fiber is then washed to obtain pure bamboo fiber and rinsing wastewater. The black liquor is then adsorbed and decolorized to obtain a decolorized solution. The decolorized solution is then acid-precipitated to release lignin, followed by a second solid-liquid separation to obtain lignin and acid-precipitated wastewater. The acid-precipitated wastewater is then oxidized (e.g., in a Fenton tank), and the effluent is desalinated by ion exchange to obtain purified water. The purified water is then mixed with the rinsing wastewater, and the resulting mixed water is reused in the soaking and boiling process.

[0085] This invention, through an integrated design of black liquor acid precipitation-oxidation-ion exchange desalination-recycling, improves the economy and environmental friendliness of the original process by changing the original process path and adding new process units. Compared with the traditional alkali process for bamboo fiber preparation (which relies on high-energy-consuming alkali recovery boilers to burn black liquor, has complex wastewater treatment, and causes secondary pollution), it achieves zero wastewater discharge throughout the entire process (all process water is recycled in a closed loop, requiring only a small amount of replenishment). At the same time, it recovers lignin from the incineration process in the traditional process into high-value chemical raw materials (purity ≥90%, used for rubber / asphalt modification), significantly improving economic benefits. Combined with an intelligent control system (precise pH / temperature / flow rate control ±0.5%), it solves the process fluctuation problem caused by manual intervention in the traditional method, improving production stability by more than 30% and reducing overall energy consumption by 35%. It completely overcomes the three major pain points of traditional technology: "high pollution, high cost, and low controllability," providing a breakthrough solution for the green upgrading of the bamboo fiber industry.

[0086] The following detailed description of the method for preparing bamboo fiber and utilizing black liquor resources provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0087] Example 1: Preparation of sulfonated lignin bamboo fiber using a sodium hydroxide-sodium sulfite system (1) The bamboo is processed into sheets with a length of 20±2mm and a thickness of 2.0±0.1mm by a bamboo splitting machine (model PS-280, Zhejiang Shuangqiang). The sheets are then fed into the pretreatment washing tank by a belt conveyor (width 500mm, speed 0.5m / s) and rinsed using countercurrent (water flow rate 2m). 3 / h) Removes impurities.

[0088] (2) In an S30408 ​​stainless steel jacketed reactor (5m³ / h) 3 In Jiangsu Aoliwei, a mixed solution of 10.5% sodium hydroxide and 1.5% sodium sulfite was added at a solid-liquid ratio of 1:18. The variable frequency stirring speed was set to 80 rpm, and the infrared temperature control system was used to maintain the temperature at 90℃ for 3 hours, then at a temperature not lower than 80℃ for 2 hours, and finally at 90℃ for 3 hours to obtain crude bamboo fiber and black liquor. The crude bamboo fiber was washed to obtain pure bamboo fiber and rinsing wastewater.

[0089] (3) After soaking and boiling, the black liquor was filtered by XZS-800 vibrating screen (Xinxiang Dahan) and then decolorized by CAL-20 activated carbon adsorption tower (Jiangsu Kangjie). The pH was adjusted to 3.0±0.1 with 98% sulfuric acid in pH adjustment tank (PE300L). Acid precipitation was carried out at 60℃ for 1.5h. The liquor was then filtered by XMY-100 plate and frame filter press (working pressure 0.6MPa) to obtain sulfonated lignin with a moisture content of 10.8% (β-O-4 bond content 68.3%, Cα sulfonic acid group 0.52mmol / g) and acid precipitation wastewater.

[0090] (4) Acid precipitation wastewater enters the Fenton reactor (processing capacity 5m³). 3 / h), according to H2O2 solution (mass concentration 30%) 1g / L, Fe 2+ Add 0.223 g / L, and after the reaction is complete, add an appropriate amount of NaOH until the iron ions are completely precipitated (this can be done by checking the pH; complete precipitation is achieved when the pH is around 8). Filter the precipitated iron ions. The COD of the effluent after the reaction is 38 mg / L. After pretreatment by a multi-media filter (quartz sand + activated carbon double layer), it is then desalinated by ion exchange (001×7 + D301 resin). After being mixed with bamboo washing wastewater (pH=10-12), it is reused in the soaking and boiling process.

[0091] The bamboo fiber yield was 79.6% (tested according to GB / T 5889-1986), the lignin recovery rate was 93.7% (determined by UV-Vis method), and the water reuse rate was 72.4%.

[0092] Example 2: Preparation of sulfur-containing lignin bamboo fiber using a sodium hydroxide-sodium sulfide system (1) Bamboo is crushed in three stages (jaw crusher + hammer crusher + fine grinding) to obtain 1.8±0.2mm thick sheets, and the pith tissue is removed by a gravity separator (model FQS-500, Sichuan Light Industry Institute).

[0093] (2) In a 316L stainless steel reactor (with variable frequency stirring at 50 rpm), a mixed solution of 11% sodium hydroxide and 1.8% sodium sulfide (solid-liquid ratio 1:17) was prepared and the solution was immersed in stages: first, it was immersed at 90℃ for 3 hours, then kept at 80℃ for 2 hours, and finally immersed at 90℃ for 3 hours. The infrared temperature control accuracy was ±0.3℃. The crude bamboo fiber and black liquor were obtained. The crude bamboo fiber was washed to obtain pure bamboo fiber and rinsing wastewater.

[0094] (3) After the black liquor temperature is slightly lower, it passes through a 200-mesh sieve in sequence, and then is adsorbed by activated carbon (iodine value ≥950mg / g) before entering the acid precipitation process: the pH is adjusted to 3.0±0.1 with 98% sulfuric acid in the pH adjustment tank (PE300L), and acid precipitation is carried out at 40℃ for 1h.

[0095] (4) After acid precipitation of black liquor, sulfur lignin (sulfur content 4.2%, thiophene structure accounting for 15.6%) is obtained. After air drying (air inlet temperature 65℃), it reaches the first grade standard of GB / T 31765-2015. Silica (SiO2 content 93.5%) is obtained by calcining silica slag in a muffle furnace at 600℃.

[0096] (5) The black liquor after acid precipitation is passed through a 200-mesh sieve in sequence → Fenton oxidation, and Fe is added. 2+ 1.5 g / L, then add 4 g / L of hydrogen peroxide solution, pH value 2, COD decreases from 12,000 mg / L to ≤150 mg / L; (6) After the Fenton reaction, add an appropriate amount of NaOH to make the solution pH=8±0.5, filter the precipitated iron mud, and the effluent is pretreated by a multi-media filter (quartz sand + activated carbon double layer) and then flows through anion and cation exchange columns for desalination. The mixed bamboo washing wastewater (pH=10-12) is then reused in the soaking and boiling process.

[0097] (7) Automatic dosing is achieved using S7-1200 PLC (pH adjustment response time 18s), the soaking temperature fluctuation is ≤0.4℃, and data is uploaded to the cloud platform via OPC-UA protocol (storage period 3 years).

[0098] Processing 1 ton of bamboo consumes 142 kWh of electricity and 1.8 tons of steam, resulting in 37% energy savings compared to traditional methods, with a water reuse rate of 82%.

[0099] Example 3: Preparation of high-purity bamboo fiber using a pure sodium hydroxide system (1) Select 3-year-old bamboo, and after ultrasonic cleaning (frequency 40kHz, power 500W) pretreatment, the slice size is controlled at 15±1mm×2.0±0.05mm.

[0100] (2) In a 10.0±0.2% sodium hydroxide solution (solid-liquid ratio 1:19), first soak and boil at 90℃ for 3 hours, then keep warm at 80℃ for 2 hours, and finally soak and boil at 90℃ for 3 hours to obtain crude bamboo fiber and black liquor; wash the crude bamboo fiber to obtain pure bamboo fiber and rinsing wastewater.

[0101] (3) After soaking and boiling, the black liquor was filtered by XZS-800 vibrating screen (Xinxiang Dahan) and then decolorized by CAL-20 activated carbon adsorption tower (Jiangsu Kangjie). The pH was adjusted to 3.0±0.1 with 98% sulfuric acid in pH adjustment tank (PE300L). Acid precipitation was carried out at 60℃ for 1.5h. The liquor was then filtered by XMY-100 plate and frame filter press (working pressure 0.6MPa) to obtain sulfonated lignin with a moisture content of 10.8% (β-O-4 bond content 68.3%, Cα sulfonic acid group 0.52mmol / g) and acid precipitation wastewater.

[0102] (4) Acid precipitation wastewater flows into the Fenton tank, and is treated with H2O2 3.2 g / L and Fe2O3 3.2 g / L. 2+ Adding 1.1 g / L further reduces COD and treats other organic pollutants.

[0103] (5) After the Fenton reaction, add an appropriate amount of NaOH to bring the solution pH to 8 ± 0.5. Filter out the precipitated iron sludge, and after pretreatment by a multi-media filter (quartz sand + activated carbon double layer), the effluent enters the ion exchange system (flow rate 5 BV / h for cation exchange and 3 BV / h for anion exchange). The final effluent contains Na + 3.8 mg / L, Cl - 7.2 mg / L, conductivity 680 μS / cm, mixed with bamboo rinsing wastewater and reused in the soaking and boiling process.

[0104] (6) The cation resin was regenerated countercurrently with 2.1% HCl (flow rate 4 BV / h), and the anion resin was regenerated cocurrently with 2.0% NaOH (preheated to 42℃). The purity of the recovered NaCl was 99.5% (XRD analysis).

[0105] The bamboo fiber has a whiteness of 82.3% (ISO 2470 standard) and a tensile strength of 1.58 GPa; each batch (100 kg) recovers 9.8 kg of industrial salt, reducing wastewater discharge by 4.7 tons.

[0106] Example 4: Preparation of highly reactive bamboo fiber using a sodium hydroxide-urea low-temperature system (1) Select 2-year-old moso bamboo, process it into sheets with a length of 25±3mm and a thickness of 1.5±0.2mm by a double roller crusher (model PG-200, Shandong Chenfa), and send it into the pre-impregnation tank by a screw conveyor (speed 15rpm).

[0107] (2) In a 316L stainless steel reactor (volume 3m³) 3 In a jacketed cooling system, a mixed solution of 8% sodium hydroxide and 12% urea (solid-liquid ratio 1:15) was prepared. The stirring speed was set to 60 rpm. The mixture was first maintained at 65±1℃ and stirred for 8 hours (temperature control accuracy ±0.5℃). Then, the power was turned off and the mixture was kept at the same temperature for 1.5 hours to obtain crude bamboo fiber and black liquor. The crude bamboo fiber was then washed to obtain pure bamboo fiber and rinsing wastewater.

[0108] (3) After the black liquor is filtered through a 200-mesh vibrating screen, it is decolorized by macroporous adsorption resin (model D101, Tianjin Nankai). The pH is adjusted to 2.8±0.1 with 85% phosphoric acid in a pH adjustment tank, and acid precipitation is carried out at 50℃ for 2 hours. The solution is then processed by a chamber filter press (working pressure 0.4MPa) to obtain low condensation lignin (β-O-4 bond content 72.1%, nitrogen element doping amount 1.2%) with a moisture content of 9.5% and acid precipitation wastewater.

[0109] (4) The acid precipitation wastewater flows into the Fenton tank, with the dosage of chemicals being 3.2 g / L H2O and Fe. 2+ Add 1.1 g / L, react for 1 hour, then add an appropriate amount of NaOH to adjust the solution pH to 8 ± 0.5. Filter to remove the precipitated iron mud. After the reaction, the COD of the effluent drops to below about 28 mg / L. After pretreatment by a multi-media filter (quartz sand + activated carbon double layer), the effluent is desalinated by anion and cation exchange resin to obtain purified water. This purified water is then mixed with bamboo washing wastewater (pH = 10-12) and reused in the soaking and boiling process.

[0110] The bamboo fiber yield is 81.3% (tested according to GB / T 5889-1986), the lignin sulfonation degree is 0.45mmol / g, the water reuse rate is 75%, and the energy consumption per ton of product is reduced by 42% compared with the traditional process.

[0111] Example 5: Synergistic preparation of high-strength bamboo fiber by sodium hydroxide-oxygen / ozone oxidation (1) The bamboo is processed into sheets with a length of 30±2mm and a thickness of 1.2±0.1mm by a slicing machine (model BQ-18, Yunnan Kunming Machinery). Light impurities are removed by wind sorting (wind speed 8m / s).

[0112] (2) In a 316L stainless steel reactor (volume 3m³) 3 In a jacketed cooling system, add a 9.5% sodium hydroxide solution (solid-liquid ratio 1:16), control the temperature at 105±1℃, and introduce oxygen (flow rate 0.2m³ / h). 3 / h), until the pressure reaches 0.3MPa, then the infrared temperature control system is adjusted to maintain the temperature at 90℃ for 3 hours, then at no less than 80℃ for 2 hours, and finally at 90℃ for 3 hours to obtain crude bamboo fiber and black liquor; the crude bamboo fiber is washed to obtain pure bamboo fiber and rinsing wastewater.

[0113] (3) After the black liquor is filtered by cross-flow through a ceramic membrane (pore size 0.1μm), it is subjected to two-stage acid precipitation (first pH=4.0, 40℃ to precipitate hemicellulose, then pH=2.0, 50℃ to precipitate lignin) and then filtered by an XMY-100 plate and frame filter press (working pressure 0.6MPa) to obtain oxidized lignin with a carboxyl content of 1.8mmol / g and a filter cake moisture content of 11.2%.

[0114] (4) Wastewater enters activated carbon for decolorization, and after desalination by anion and cation exchange resins, it undergoes ozone catalytic oxidation (ozone dosage 20g / L, COD concentration 5000mg / L). The effluent COD ≤ 25mg / L, SS ≤ 5mg / L, and all of it is recycled for raw material pretreatment.

[0115] The bamboo fiber has a crystallinity of 68.4% (XRD analysis) and a tensile strength of 1.82 GPa, achieving zero wastewater discharge.

[0116] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing bamboo fiber and utilizing black liquor resources, characterized in that, The method comprises the following steps: immersing bamboo chips in an alkali liquor, first solid-liquid separation, to obtain crude bamboo fibers and black liquor; washing the crude bamboo fibers to obtain pure bamboo fibers and washing wastewater; purifying the black liquor to obtain purified water; mixing the purified water and the washing wastewater, and recycling the mixed water to the immersing step; the purifying is carried out by method 1 or method 2; the method 1 comprises the following steps: adsorbing and decoloring the black liquor to obtain decolorized liquor; acidifying the decolorized liquor to precipitate lignin, second solid-liquid separation, to obtain lignin and acidification wastewater; performing Fenton oxidation on the acidification wastewater, and then performing ion exchange desalination to obtain purified water; the method 2 comprises the following steps: acidifying the black liquor to precipitate lignin, second solid-liquid separation, to obtain lignin and acidification wastewater; performing adsorption and decoloring, ion exchange desalination, and then ozone oxidation on the acidification wastewater to obtain purified water.

2. The method of claim 1, wherein, The alkali agent in the alkali liquor is sodium hydroxide, or a sodium hydroxide-sodium sulfite composite alkali agent, or a sodium hydroxide-sodium sulfide composite alkali agent, or a sodium hydroxide-urea composite alkali agent; when the alkali agent is sodium hydroxide, the mass concentration of the alkali liquor is 8-12%; when the alkali agent is a sodium hydroxide-sodium sulfite composite alkali agent, the mass concentration of sodium hydroxide in the alkali liquor is 6-12%, and the mass concentration of sodium sulfite is 0.5-1.5%; when the alkali agent is a sodium hydroxide-sodium sulfide composite alkali agent, the mass concentration of sodium hydroxide in the alkali liquor is 6-12%, and the mass concentration of sodium sulfide is 0.5-2%; when the alkali agent is a sodium hydroxide-urea composite alkali agent, the mass concentration of sodium hydroxide in the alkali liquor is 8-12%, and the mass concentration of urea is 12-15%; when the alkali agent is sodium hydroxide, or a sodium hydroxide-sodium sulfite composite alkali agent, or a sodium hydroxide-sodium sulfide composite alkali agent, the immersing comprises: first immersing at 90-105℃ for 3-4h, then keeping warm at not less than 80℃ for 1-2h, and finally immersing at 90-105℃ for 3-4h; when the alkali agent is a sodium hydroxide-urea composite alkali agent, the immersing comprises: first constant-temperature stirring immersing at 65±1℃ for 8-10h, then keeping warm and standing for 1.5-4h after power-off.

3. The method of claim 1, wherein, The adsorbent used in the adsorption and decoloring comprises activated carbon or macroporous adsorption resin.

4. The method of claim 1, wherein, when method 1 is used for purifying, the acidifying is first-stage acidifying; the first-stage acidifying is carried out at a temperature of 40-60℃, a pH value of 2-4, and for a time of 1-2h; when method 2 is used for purifying, the acidifying is two-stage acidifying; the two-stage acidifying comprises sequentially carrying out first-stage acidifying and second-stage acidifying; the first-stage acidifying is carried out at a temperature of 35-40℃, a pH value of 4-5, and for a time of 3-4h; the second-stage acidifying is carried out at a temperature of 40-60℃, a pH value of 2, and for a time of more than 6h.

5. The method of claim 1, wherein, the ozone oxidation comprises: adjusting the pH value of the acidification wastewater to 9-10, and carrying out ozone aeration on the acidification wastewater in the presence of a catalyst; the ozone oxidation is carried out for a time of 1-2h; the mass concentration ratio of ozone to COD is 4-5:

1.

6. The method of claim 1, wherein, The Fenton oxidation is homogeneous Fenton oxidation or heterogeneous Fenton oxidation. The conditions of the homogeneous Fenton oxidation include: Fe 2+ The dosage is 0.22-1.5 g / L, the dosage of hydrogen peroxide solution is 0.5-4 g / L, and the pH value is 2-4; The conditions of the heterogeneous Fenton oxidation include: the iron-based catalyst dosage is 0.5-2 g / L, the hydrogen peroxide solution dosage is 2-4 g / L, and the pH value is 2-4. The mass concentration of the hydrogen peroxide solution is 30%.

7. The method of claim 1, wherein, The process parameters of the Fenton oxidation, the ozone oxidation and the acid separation are intelligently controlled.

8. The method of claim 1, wherein, The second solid-liquid separation includes pressure filtration or rotary vibration screen filtration.

9. The method of claim 1, wherein, The ion exchange desalination comprises removing Na + and Cl - from the solution by using strong acid cation exchange resin and weak base anion exchange resin successively.

10. The method of claim 1, wherein, The water supplementing amount of the immersion boiling and the temperature of the immersion boiling are controlled by PLC.

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